Detect btrfs and overlayfs filesystems and automatically fall back to sequential
mode to prevent deadlocks caused by SQLite WAL file locking and btrfs COW copy-up
locks when multiple forked workers try to access the same files simultaneously.
The fix adds a _is_btrfs_or_overlayfs() function that:
1. Attempts to detect the filesystem type using stat command
2. Falls back to reading /proc/mounts if stat fails
3. Returns True if the filesystem is btrfs or overlayfs
The sequential mode condition is updated to include this check, ensuring that
on affected filesystems, all features run in a single process instead of being
split across multiple forked workers.
ISSUES CLOSED: #9390
HAL9000
Test